Polar semiconductor hole transporting material

ABSTRACT

A semiconductive hole transport material containing polar substituent groups, the polar substituent groups substantially not affecting the electronic properties of the hole transport material and the hole transport material being soluble in a polar solvent.

The present invention is concerned with methods for making an organicelectronic device. The present invention also is concerned withelectronic devices preparable by the present methods. The presentinvention also is concerned with hole transport materials for use inelectronic devices and to methods for making the same.

Such organic devices include organic light-emitting diodes (OLEDs). Oneor more of the layers in the device typically will comprise a polymer.Further, such devices typically comprise one or more semiconductivepolymer layers located between electrodes. Semiconductive polymers arecharacterised by partial or substantial pi-conjugation in the backboneor side chains.

Semiconductive polymers are now frequently used in a number of opticaldevices such as in polymeric light emitting devices (“PLEDs”) asdisclosed in WO 90/13148; field effect transistors (“FETs”);photovoltaic devices as disclosed in WO 96/16449; and photodetectors asdisclosed in U.S. Pat. No. 5,523,555.

A typical LED comprises a substrate, on which is supported an anode, acathode, and an organic electroluminescent layer located between theanode and cathode and comprising at least one electroluminescentmaterial. In operation, holes are injected into the device through theanode and electrons are injected into the device through the cathode.The holes and electrons combine in the organic electroluminescent layerto form an exciton, which then undergoes radiative decay to give light.Other layers may be present in the LED. For example a layer of organichole injection material such as poly(ethylene dioxythiophene) (PEDT)doped with a charge balancing dopant may be provided between the anodeand the organic electroluminescent layer to assist injection of holesfrom the anode to the organic electroluminescent layer. The chargebalancing dopant may be acidic. The charge balancing dopant may be apolyanion. Preferably the charge balancing dopant comprises a sulfonate,such as poly(styrene sulfonate) (PSS).

Further, a layer of an organic hole transport material may be providedbetween the anode (or the hole injection layer where present) and theorganic electroluminescent layer to assist transport of holes to theorganic electroluminescent layer.

Generally, it is desired that the polymer or polymers used in theafore-mentioned organic devices are soluble in common organic solventsto facilitate their deposition during device manufacture. Many suchpolymers are known. One of the key advantages of this solubility is thata polymer layer can be fabricated by solution processing, for example byspin-casting, ink-jet printing, screen-printing, dip-coating etc.Examples of such polymers are disclosed in, for example, Adv. Mater.2000 12(23) 1737-1750 and include polymers with at least partiallyconjugated backbones formed from aromatic or heteroaromatic units suchas fluorenes, indenofluorenes, phenylenes, arylene vinylenes,thiophenes, azoles, quinoxalines, benzothiadiazoles, oxadiazoles,thiophenes, and arylamines with solubilising groups, and polymers withnon-conjugated backbones such as poly(vinyl carbazole). Polyarylenessuch as polyfluorenes have good film forming properties and may bereadily formed by Suzuki or Yamamoto polymerisation which enables a highdegree of control over the regioregularity of the resultant polymer.

In certain devices, it can be desirable to cast multiple layers, i.e.,laminates, of different materials (typically polymers) on a singlesubstrate surface. For example, this could be to achieve optimisation ofseparate functions, for example electron or hole charge transport,luminescence control, photon-confinement, exciton-confinement,photo-induced charge generation, and charge blocking or storage.

In this regard, it can be useful to be able to fabricate multilayers ofmaterials (such as polymers) to control the electrical and opticalproperties, for example, across the device. This can be useful foroptimum device performance. Optimum device performance can be achieved,for example, by careful design of the electron and hole transport leveloffset, of the optical refractive index mismatch, and of the energy gapmismatch across the interface. Such heterostructures can, for example,facilitate the injection of one carrier but block the extraction of theopposite carrier and/or prevent exciton diffusion to the quenchinginterface. Thereby, such heterostructures can provide useful carrier andphoton confinement effects.

However, preparation of polymer laminates generally is not trivial. Inparticular, the solubility of initially cast or deposited layers in thesolvents used for succeeding layers can be problematic. This is becausesolution deposition of the subsequent layer can dissolve and destroy theintegrity of the previous layer.

One option for overcoming this problem is to work with precursor polymersystems. Precursor systems of PPV (polyphenylene vinylene) and PTV(polythienylene vinylene) are known in this art.

Layers of semiconducting polymers may be formed by depositing a solublepolymeric precursor which is then chemically converted to an insoluble,electroluminescent form. For example, WO 94/03030 discloses a methodwherein insoluble, electroluminescent poly(phenylene vinylene) is formedfrom a soluble precursor and further layers are then deposited fromsolution onto this insoluble layer.

However, it is clearly undesirable to restrict the polymer in a polymerdevice to that class of polymers that may be formed from insolubleprecursor polymers. Furthermore, the chemical conversion processrequired for precursor polymers involves extreme processing conditionsand reactive by-products that may harm the performance of the priorlayers in the finished device.

A number of publications disclose devices where two layers are solutionprocessed during device manufacture such that the solvent use for thesecond layer does not dissolve the first layer.

One approach is to form the first layer and then to crosslink the firstlayer to render it insoluble so that the second layer then can beformed.

WO96/20253 generally describes a luminescent film-forming solventprocessable polymer which contains crosslinking. It is stated thatbecause the thin films resist dissolution in common solvents thisenables deposition of further layers, thereby facilitating devicemanufacture. The use of azide groups attached to the polymer main chainis mentioned as an example of thermal crosslinking.

U.S. Pat. No. 6,107,452 discloses a method of forming a multilayerdevice wherein fluorene containing oligomers comprising terminal vinylgroups are deposited from solution and cross-linked to form insolublepolymers onto which additional layers may be deposited.

Similarly, Kim et al, Synthetic Metals 122 (2001), 363-368 disclosespolymers comprising triarylamine groups and ethynyl groups which may becross-linked following deposition of the polymer.

Problems exist with these crosslinking methods since the device must besubjected to crosslinking conditions e.g. heating after the depositionof a layer. This can have detrimental effects on the already depositedlayer. Crosslinking methods also can result in side products, which cancontaminate the film. Further, disadvantageous side radical reactionscan occur. These side radical reactions result in less than the maximumdegree of crosslinking being obtained and the functionality of thepolymer being affected.

WO 2004/023573 is concerned with a method of forming an optical devicecomprising the steps of providing a substrate comprising a firstelectrode capable of injecting or accepting charge carriers of a firsttype; forming over the first electrode a first layer that is at leastpartially insoluble in a solvent by depositing a first semiconductingmaterial that is free of cross-linkable vinyl or ethynyl groups and is,at the time of deposition, soluble in the solvent; forming a secondlayer in contact with the first layer and comprising a secondsemiconducting material by depositing a second semiconducting materialfrom a solution in the solvent; and forming over the second layer asecond electrode capable of injecting or accepting charge carriers of asecond type wherein the first layer is rendered at least partiallyinsoluble by one or more of heat, vacuum and ambient drying treatmentfollowing deposition of the first semiconducting material.

JP 2003-217863 takes a different approach. In particular, thisdisclosure teaches the presence of a compound in a solution depositedlayer, where the compound can render the layer insoluble upon heating.In one example, a hole transport layer of F8 doped with an electronacceptor of an antimony hexachloride salt of tri(bromophenyl) amine isused. The layer is deposited from tetrahydrofuran and insolubilised byheating at 100° C. for 20 hours. An emissive layer of F8 then isdeposited from xylene solution. Doping of the F8 polymer alters itscharge transporting properties, providing it with hole transportingfunctionality. However if a soluble material that possesses suitablehole transporting functionality is treated with a doping agent, thenthis will result in an undesirable alteration of that functionality.

A further option for overcoming this problem is to use polymersmaterials that differ widely in their solubility behaviour so that adifferent solvent (in which the first layer is not soluble) can be usedto deposit the second layer. Again, this option severely restricts theclasses of materials that can be used in a multilayered stack. This isbecause most conjugated polymer systems are characterised by solubilityin the same set of hydrocarbon solvents (such as xylenes and othersubstituted benzenes and tetrahydrofuran, and halogenated solvents).

For example, the use of a polymer that is soluble in a hydrocarbonsolvent in conjunction with a polymer that is soluble in water or in anacetate solvent can allow the preparation of a limited bilayer ortrilayer stack. An important example in this respect is the depositionof a conjugated polymer from an aromatic hydrocarbon solvent over afirst-formed conductive PEDT:PSS film that is not soluble in thearomatic hydrocarbon solvent.

US 2002/096995 discloses the following multilayer structure in Example1:

-   -   ITO;    -   —Poly(ethylene dioxythiophene)/poly(styrene sulfonate)        “PEDT/PSS”;    -   emissive layer of Ir(ppy)₃/“PVK” by spin coating from        1,2-dichloroethane;    -   electron transport layer of        1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene        “TPBI”/polyvinylbutyryl binder by spin coating from 1-butanol.

JP 2002-050482 is concerned generally with providing a high brightness,efficient, organic LED. Generally, this disclosure is concerned with anorganic light-emitting device with two different luminescent layers. Thefirst luminescent layer contains an ortho-metallated complex and has afirst emission spectrum and the second luminescent layer contains amacromolecule which has a different emission spectrum from the firstluminescent layer. This arrangement is said to lead to an efficientdevice with high brightness. The following multilayer structure isdisclosed in Example 1:

-   -   ITO;    -   poly(ethylene dioxythiophene) “PEDT”;    -   “First luminous layer” of Ir(ppy)₃/poly(N-vinylcarbazole) “PVK”        deposited by spin coating from 1,2-dichloroethane;    -   “Second luminous layer” of a blend of poly(9,9′ n-octyl        fluorene) “F8”, F8-amine copolymer and a diazole deposited by        spin-coating from xylene solution.

JP 2003-077673 also is concerned with achieving high brightness andefficiency in organic electroluminescent devices. In one example in JP2003-077673, a device has a hole transport layer, an emissive layer andan electron transport layer. The device is formed by solution processingof two of the layers wherein the solvent used for the emissive layerdoes not dissolve the hole transport layer and/or the solvent used forthe emissive layer does not dissolve the electron transport layer. Inone example, the device structure is as follows:

-   -   hole transport layer of PVK formed by spin-coating from        1,2-dichloroethane;    -   emissive layer of F8/Ir(ppy)₃ formed by spin-coating from        xylene;    -   electron transport layer Alq formed by evaporation.

JP 2002-319488 is concerned with avoiding problems associated with usingvacuum over evaporation during device manufacture. In Example 1, thefollowing multilayer structure is used:

-   -   hole transport layer of PVK formed by spincoating from        1,2-dichloroethane;    -   emissive layer of polystyrene/polyvinyl biphenyl “PBD”/Ir(ppy)₃        formed by spin-coating from cyclohexane.

In Example 3, the following multilayer structure is used:

-   -   hole transport layer of PVK formed by spin-coating from        1,2-dichloroethane;    -   emissive layer of polyvinyl biphenyl/“OXD-1”/Ir(ppy)₃ formed by        spin-coating from xylene; “OXD-1” is defined in JP 2002-319488;    -   electron transport layer of polystyrene/PBD deposited from        cyclohexane.

JP 2003-007475 again is concerned with providing an efficientelectroluminescent element with high brightness. In particular, thisdisclosure is concerned with lowering the voltage needed to drive thedevice. The following multilayer structure is disclosed:

-   -   hole transport layer of dibutyl fluorene deposited from        1,2-dichloroethane;    -   emissive layer of “polyvinyl biphenyl”/carbazole biphenyl        “CBP”/Ir(ppy)3 formed by spin-coating from xylene;    -   electron transport layer of OXD-1 as defined in JP 2003-007475        formed by evaporation.

In these disclosures, the devices are designed within the confines ofselecting materials with the desirable solubility behaviour so thatlaminates may be made. It will be appreciated that limitations on thematerials that are useable in the laminate mean that many concepts ofdevice structure cannot be investigated or implemented. As such, thefurther development of device architecture may become heavily impeded.

J. Am. Chem. Soc. 1996, 118, 7416-7417 discloses the use of BDOH-PF in asingle layer LED and LEC. BDOH-PF is soluble in THF and toluene andother common organic solvents. An LED is fabricated by sandwiching athin film of BDOH-PF (as the emitter) between an ITO-coated glass anodeand a vacuum evaporated cathode. An LEC is fabricated using a blend ofBDOH-PF with lithium triflate. A thin film of the blend was sandwichedbetween and ITO-coated glass anode and a vacuum evaporated aluminiumfilm.

WO 01/47043 is concerned with a method for forming a transistorcomprising: depositing a first material from solution in a firstsolvent; and subsequently whilst the first material remains soluble inthe first solvent, forming a second layer of the transistor bydepositing over the first material the second material from solution ina second solvent in which the first material is substantially insoluble.According to one preferred embodiment described on page 4 of WO 01/47043one of the first and second solvents is a polar solvent and the other ofthe first and second solvents is a non-polar solvent. As such, one ofthe first and second layers may be a non-polar polymer layer that issoluble in a non-polar solvent and the other of the first and secondlayers may be a polar polymer layer that is soluble in a polar solvent.There is no mention of a hole transport material or a hole transportlayer. As described above, the invention that is the subject of WO01/47043 works within the confines of selecting materials with thedesirable solubility behaviour, thus, similar limitations exist on thematerials that are useable in the invention according to WO 01/47043.

Chem. Mater., 2004, 16, 708-716 discloses two conjugatedpolyelectrolytes (P2, P4), which are soluble in polar solvents. Further,J. Am. Chem. Soc., 2004, 126 (31), 9845-9853 discloses the quarternisedammonium polyelectrolyte derivatives of a series ofaminoalkyl-substituted polyfluorene copolymers with benzothiadiazole,which were synthesised by the Suzuki coupling reaction. The quarternisedpolymers are soluble in DMSO, methanol, and DMF. It is said that thesolubility of these quarternised polymers in alcohol offers anopportunity of fabricating multilayer polymer LEDs by spin coating fromsuch solvents, since most of the electroluminescent polymers and carriertransporting materials are not soluble in the alcohol.

Reference may also be made to U.S. Pat. No. 5,900,327, which disclosesthe use of fluorenes and polyfluorenes having one or two polarsubstituents, for use as luminescent materials in organic light-emittingdevices.

WO 99/48160 is concerned with an electroluminescent device comprising afirst charge carrier injecting layer for injecting positive chargecarriers; a second charge carrier injecting layer for injecting negativecharge carriers; and a light-emissive layer located between the chargecarrier injecting layers and comprising a mixture of a first componentfor accepting positive charge carriers from the first charge carrierinjecting layer; a second component for accepting negative chargecarriers from the second charge carrier injecting layer; and a third,organic light-emissive component for generating light as a result ofcombination of charge carriers from the first and second components. Atleast one of the first, second and third components forms a type IIsemiconductor interface with another of the first, second and thirdcomponents.

In view of the above it will be understood that there still remains aneed to provide further methods for fabricating multilayer organic(typically polymer) electronic devices.

As such, it is an aim of the present invention to provide a new methodfor organic electronic device manufacture, preferably that is compatiblewith high performance. Further it is an aim of the present invention toprovide devices obtainable by the new method.

The present invention provides new means for controlling the processingproperties of materials used in the manufacture of multilayer organic(typically polymer) electronic devices. The new means comprise theintroduction by design of polar groups into a material to alter thesolubility behaviour of that material, thereby rendering it soluble inpolar solvents.

Thus, the present invention provides a method of controlling theprocessing properties of a material for use in an organic electronicdevice, comprising the step of:

forming a material comprising polar substituent groups in a mannerenabling it to be laid down as a film by solution processing from apolar solvent,

where the polar substituents control the processing properties of thematerial to render it soluble in the polar solvent.

For optimising solution processing, particularly ink jet printing, amixture of solvents may be present.

According to the present invention, the number and nature of polarsubstituent groups are selected so as to control the processingproperties of the material to render it soluble in a polar solvent. Thismay be contrasted with prior art materials containing polar substituentgroups, where the polar substituent groups are not present by design forthe purpose of controlling the processing properties of the material.

The method outlined above of controlling the processing properties of amaterial, can be considered to be the inventive concept underlying thepresent invention and can be applied in practice in several methods ofdevice manufacture. These include those discussed below in relation tothe first, second, third, fourth and sixth aspects of the invention.

In accordance with the first aspect, the method of controlling theprocessing properties is applied to a hole transport material byincorporating polar substituent groups thereinto.

Thus the first aspect of the present invention provides, a method forforming an organic electronic device, including the steps of:

depositing a semiconductive hole transport material from solution in apolar solvent to form a hole transport layer of the device; andsubsequently

forming a second layer of the device by depositing on the hole transportlayer a second material from solution in a non-polar solvent in whichthe hole transport layer is substantially insoluble; and

characterised in that the hole transport material contains polarsubstituent groups selected so that the hole transport material issoluble in the polar solvent, the second material being substantiallyinsoluble in the polar solvent.

For optimising solution processing, particularly ink jet printing, amixture of solvents may be present in the afore-mentioned solutions.

It will be understood that advantageously, the step of forming thesecond layer can be carried out whilst the hole transport materialremains soluble in the polar solvent. Thus, there is no need tocrosslink the hole transport material after deposition.

Unlike for an emissive material, any change in the emission spectrum ofthe hole transport material that is caused by the incorporation of thepolar substituent groups is not of consequence to device performance.Further, rendering a hole transport material soluble in polar solventsbut insoluble in non-polar solvents enables deposition of the subsequent(typically emissive) layer from a non-polar solvent. This isadvantageous since most known emissive materials are soluble innon-polar solvents.

As mentioned above, historically, preferred polymers used in organicelectronic devices have been soluble in common organic solvents, such asalkylated benzenes, in particular xylene, and toluene. Such polymers areinsoluble in polar solvents. Therefore, according to the present methodthe integrity of a hole transport material whose processing propertieshave been controlled in accordance with the present invention will notbe affected by the deposition thereon of a polymer in a common organicsolvent.

The polar substituent groups are covalently attached to the holetransport material. In the absence of the polar substituent groups, thehole transport material still is capable of hole transport. Thus, thepolar substituent groups substantially do not affect the electronicproperties of the hole transport material.

Typically, the hole transport material is soluble in common organicsolvents in the absence of the polar substituents.

The presence of the polar substituent groups preferably substantiallydoes not affect the electronic properties of the hole transportmaterial. In other words the hole transporting capabilities of thematerial comprising the polar substituent groups preferablysubstantially are the same as the hole transporting capabilities of theequivalent material without the polar substituent groups.

Preferably, the hole transport material has a pH less than or equal to3.

In the method according to the first aspect of the present invention,the hole transport material preferably comprises a hole transportpolymer. However, the material is not so limited and can be, forexample, a small molecule, dendrimer or a metal complex.

When the hole transport material comprises a polymer, it desirably is acopolymer or higher order polymer (e.g. terpolymer). Thus, the polarsubstituent groups can be present on all or on only some of the repeatunits. The hole transport polymer preferably comprises a repeat unitcomprising an aryl or heteroaryl group. Preferably, the aryl orheteroaryl group is in the polymer backbone.

Still further, in the method according to the first aspect of thepresent invention, in some embodiments, the hole transport materialpreferably is conjugated. In the case of a polymer, in theseembodiments, the polymer preferably is partially or fully conjugatedalong the polymer backbone.

It is preferred that there is a break in the conjugation between eachpolar substituent group and the conjugated segment or segments of thematerial. This helps to minimise the effect of the polar substituentgroups on the electronic properties of the material. To this end, aspacer group may be introduced between a polar substituent group and theconjugated segment or segments of the material. Suitable spacer groups(x and x′) comprise saturated hydrocarbyls such as (CH2)n where n is inthe range of from 1 to 5, preferably in the range of 1 to 3.

When the hole transport material comprises a polymer, it is preferredthat the polar substituent groups are not in conjugation with thepolymer backbone. It is preferred that the polar substituent groups arecomprised in side chains or side groups pendant from the backbone of thepolymer. Each side chain or side group may comprise one or more, forexample two, polar substituent groups.

Preferred spacer groups include aryl and heteroaryl groups such asphenyl; alkyl groups, for example (CH2)n where n is from 2 to 10,preferably 2 to 4; alkoxy groups, for example O(CH2)n′ where n′ is from2 to 10, preferably 4; perfluoroalkyl groups, for example (CF2)n2 wheren2 is from 2 to 10; and perfluoroalkoxy groups, for example O(CF2)n3where n3 is from 2 to 10.

In one embodiment, a conjugated spacer group is preferable, for examplea spacer group comprising an aryl or heteroaryl group, such as phenyl.In this embodiment, each aryl or heteroaryl group can carry one or more(for example two) polar substituent groups.

A preferred hole transport polymer is a fluorene-containing polymer inwhich all or a proportion of the fluorene groups carry the polarsubstituent groups.

Other preferred aryl and heteroaryl repeat units to be present in thepolymer are those comprising a group selected from a spirofluorene,indenofluorene, p-linked dialkyl phenylene, a p-linked disubstitutedphenylene, a phenylene vinylene, a 2,5-linked benzothiadiazole, a2,5-linked substituted benzothiadiazole, a 2,5-linked disubstitutedbenzothiadiazole, a 2,5-linked substituted or unsubstituted thiophene ora triarylamine. These groups can be used to further tune the processingproperties of the polymer and optionally can carry non-polar and/orpolar substituent groups.

Preferably, the hole transporting polymer comprises triarylamine repeatunits. More preferably, it is a copolymer comprising a first, arylene,repeat unit and a second, triarylamine, repeat unit.

Preferably each of the polar substituents is bound to a first, arylene,repeat unit.

Suitable triarylamine repeat units are selected from repeat units offormulae 7-12:

Wherein A′, B′, A, B, C and D are independently selected from H or asubstituent group. More preferably, one or more of A′, B′, A, B, C and Dis independently selected from the group consisting of alkyl, aryl,perfluoroalkyl, thioalkyl, cyano, alkoxy, heteroaryl, alkylaryl andarylalkyl groups. Most preferably, A′, B′, A and B are C1-10 alkyl. Oneor more phenyl groups of repeat units 7 to 12 may optionally be linked.Preferably, the hole transporting material has a HOMO level in the rangeof about 4.8-5.5 eV.

Referring to the polar substituent groups, the number and nature ofpolar substituent groups will affect the ultimate solubility of the holetransport material. Where the hole transport material is a polymer, in aselected proportion of the monomers used to make the polymer, eachmonomer comprises at least one polar substituent group. Preferably forabout 5 to 90%, more preferably 30-50%, of the monomers, each monomercontains at least one polar substituent group. For each monomercontaining at least one polar substituent group, the residue of themonomer that is incorporated into the polymer as a repeat unit willcontain the at least one polar substituent group. Each repeat unit maycomprise one or more polar substituent groups. In the case of an ABcopolymer it is preferred that one of the repeat units (A or B)comprises one polar substituent group (i.e. the proportion of repeatunits comprising a polar substituent group equals 50%).

The polar substituent groups may be charged or neutral. Examples ofunits comprising (a) neutral and (b) charged and polar substituentgroups are set out below.

(a) Neutral Polar Substituent Groups

Preferred neutral polar substituent groups are hydrophilic groups. Evenmore preferred neutral polar substituent groups are non-labilehydrophilic groups. These groups have the advantage that small leavinggroups will not break from the polar group in the system. Such freeleaving groups can have detrimental effects on device performance.

It is to be noted that the presence of non-polar and/or hydrophobicsubstituent groups in the hole transport material is not precluded. Onthe contrary, the presence of non-polar and/or hydrophobic substituentgroups can further tune the processing properties of the hole transportmaterial.

Preferred neutral polar substituent groups independently can be selectedfrom aliphatic or alicyclic oxygen-, nitrogen-, sulphur- andphosphorous-containing groups known in the art. For exampleoxygen-containing groups include ether (particularly polyether), esterand aldehyde (including polyaldehyde). Nitrogen-containing groupsinclude amine (primary, secondary and tertiary), cyano, amide, andimine. Polyamines are preferred. Sulphur-containing groups includethiophene, thiol, and mercapto. Phosphorous-containing groups includephosphine and phosphazene.

Particularly preferred polar groups include groups containing an oxygenor nitrogen atom.

Preferred polar groups are amines, in particular cyclic amines, such asmorpholine; and ethers comprising at least 3 oxygen atoms. Otherpreferred polar groups include non-conjugated pyridines, such as alkylpyridines.

A neutral polar substituent group may become charged in situ, afterdeposition of the hole transport layer, thus becoming a charged polarsubstituent group.

In one embodiment it is preferred for the polar substituent groups(either charged or neutral) to be present as substituents at the 9position of fluorene repeat units of the type described in WO 02/092723.

An example of a fluorene-containing polymer comprises a repeat unitcomprising general formula 1:

where x and x′ are optional spacer groups as defined anywhere herein; Rand R′ are polar substituent groups and n4 and n5 each independently isin the range of from 0 to 10, preferably 0 to 5.

In one embodiment it is preferred that at least one of x and x′comprises at least one substituted or unsubstituted aryl or heteroarylgroup. In this regard, reference is made to WO 02/092723.

In general formula 1, x and x′ may represent phenyl.

In general formula 1, R and R′ may independently represent oligoether.For neutral polar substituent groups, it is preferred that R and R′ eachindependently comprises a unit of formula:

R″O—(CH2CH2O)p-

wherein R″ is H or an optionally substituted hydrocarbyl group,preferably an alkyl, phenyl or alkylphenyl group and p is at least 2.

Examples of groups having general formula 1 are shown below in formulae2 to 6b:

where n4 and n5 are as defined anywhere herein and each R8 independentlyrepresents alkyl, preferably C1 to C10 alkyl, more preferably methyl.

(b) Charged Polar Substituent Groups

Preferably the charged polar substituent groups contained in the holetransport polymer comprise a plurality of groups XY with a highdissociation constant such that each group effectively is ionisedcompletely (X^(⊖)Y^(⊕)). Typically, group XY enhances the watersolubility of the composition.

Preferably, XY is a group having a dissociation constant of greater than10-12. XY may represent a strong acid or a salt.

Suitable polar groups further include acid groups; alcohols (includingpolyalcohols); and aldehydes (including polyaldehydes).

XY may represent —SO3Y. Counterion Y may be H (i.e. sulfonic acid), or ametal cation, in particular K or Na.

XY may represent a carboxylic acid or an acrylic acid.

Y may represent a quaternized or protonated non-conjugated pyridine.

XY may represent a quaternized salt; for example having formulaX^(⊖⊕)N(R²R³R^({dot over (4)})) where X represents an anion such as ahalide, preferably Br or tetrafluorborate BF4- or hexafluorophosphatePF6-. R2, R3 and R4 independently represent alkyl, preferably C1 to C10alkyl, more preferably methyl.

A preferred quaternized salt is

XY may comprise a protonated amine, for example amine protonated bysulfonic acid such that Y represents a sulfonate ion.

X may represent a charged sulphur-containing group, in particularsulfonate, sulfate, sulfite and sulfide.

X may represent a charged phosphorus-containing group, in particularphosphate.

In a preferred embodiment, the substituent XY is provided as asubstituent R or R′ in a polymer comprising a repeat unit of generalformula 1 above.

As stated above, the number and nature of polar substituent groups willaffect the ultimate solubility of the hole transport material. In somecases, neutral polar substituent groups may render the hole transportmaterial soluble in polar solvents without rendering it substantiallyinsoluble in non-polar solvents. It is therefore preferred that the holetransport material according to the first aspect of the invention isrendered substantially insoluble in the non-polar solvent bysubstitution of the polar solvent with a charged polar substituentgroup. It will be appreciated that the extent of solubility of anymaterial in polar or non-polar solvents may readily be determined bysolubility experiments.

When the hole transport material comprises a polymer, said polymer maycomprise regions, each region having a HOMO energy level and a LUMOenergy level that are distinct from the HOMO and LUMO energy level ofthe other regions. In view of the distinct HOMO and LUMO energy levels,each region is functionally distinct.

The hole transport polymer may contain one or more hole transportregions. The hole transport polymer or a hole transport region in thehole transport polymer preferably has a HOMO energy level of at least4.8 eV, more preferably in the range 4.8 to 6 eV, still more preferablyin the range 4.8 to 5.5 eV.

The hole transport polymer preferably comprises an aryl or heteroarylrepeat group Ar. The aryl or heteroaryl repeat groups may be present inthe polymer backbone. The aryl or heteroaryl repeat groups may bepresent in side groups pendant from the polymer backbone. When Ar ispresent in a side group that is pendant from the polymer backbone, theside group may be attached to a non-conjugated or conjugated region inthe polymer backbone.

The backbone of the hole transport polymer may have regions ofconjugation. The regions of conjugation may be broken by regions ofnon-conjugation. The backbone may be fully conjugated or fullynon-conjugated. A conjugated region consists of one or more conjugatedgroups in the backbone. A non-conjugated region consists of one or morenon-conjugated groups in the backbone.

The polar substituent groups may be pendant from a non-conjugated regionof the polymer backbone.

The polar substituent groups may be pendant from a conjugated region ofthe polymer backbone.

Preferably, when the hole transport material comprises a polymer, thepolar substituent groups are present as substituents on side groupspendant from the polymer backbone.

Ar repeat groups in the hole transport polymer advantageously can befunctional repeat groups in the polymer. In other words, the Ar repeatgroups may give rise to the hole transporting properties of the polymer.When the Ar repeat groups are present in the polymer backbone they maygive rise to hole transporting properties along the backbone.

The Ar repeat groups in the hole transport polymer may give rise toemissive properties.

Ar may represent any suitable aryl or heteroaryl group. Ar may representan optionally substituted hydrocarbyl aryl group, in particular fluorene(particularly 2,7-linked fluorene), spirofluorene, indenofluorene,phenylene, or phenylenevinylene. Ar may represent an optionallysubstituted heteroaryl group, in particular thiophene orbenzothiadiazole. Ar may represent an optionally substituted (e.g.alkylated) triarylamine group, in particular triphenylamine. Ar mayrepresent an optionally substituted carbazole group. Ar may be selectedaccording to desired charge transport and/or emissive properties for thehole transport polymer.

Ar may be substituted. Examples of substituents include solubilisinggroups; electron withdrawing groups such as fluorine, nitro or cyano;and substituents for increasing glass transition temperature (Tg) of thepolymer.

In order to confer hole transporting properties on the polymer, it ispreferred that Ar comprises an optionally substituted triarylamine or anoptionally substituted carbazole.

In one embodiment, the hole transport polymer contains a repeat sidegroup comprising formula 13:

where Ar represents an aryl or heteroaryl group and R represents a polarsubstituent group as defined anywhere herein.

The polar substituent group R may be charged or neutral. Where R is acharged polar substituent group, the hole transport polymer may comprisea repeat side group comprising formula 14:

where Ar represents an aryl or heteroaryl group and XY represents agroup with a high dissociation constant, such that it effectively isionised completely (X^(⊖)Y^(⊕)):

Ar in formula 13 may represent phenyl or biphenyl. The repeat side groupmay comprise formula 17 or 18:

where R represents a polar substituent group as defined anywhere hereinand

R7 represents H or a substituent group. Examples of substituents includesolubilising groups such as C1-20 alkyl or alkoxy; electron withdrawinggroups such as fluorine, nitro or cyano; and substituents for increasingglass transition temperature (Tg) of the polymer.

In formula 17 and 18, R preferably represents XY.

Ar in formula 13 may represent triphenylamine. The repeat side group maycomprise formula 19:

where R represents a polar substituent group as defined anywhere herein.Preferably R represents XY.

In one embodiment, the repeat side group is pendant from anon-conjugated group in the backbone. For example, the hole transportpolymer may comprise a repeat unit of formula 20:

where the side group Ar—R is as defined anywhere herein, for example asshown in formula 21 or formula 22:

The hole transport polymer may comprise a copolymer comprising a firstrepeat unit as shown in any one of formulae 20 to 22 and a secondrepeat. The second repeat unit may have formula 23 or 24:

where Ar is as defined anywhere herein.

where R7 represents H or a substituent group. Examples of substituentsinclude solubilising groups such as C1-20 alkyl or alkoxy; electronwithdrawing groups such as fluorine, nitro or cyano; and substituentsfor increasing glass transition temperature (Tg) of the polymer.

Polymers with a part or the whole of the backbone being non-conjugatedmay be formed by polymerising the repeat units, which formnon-conjugated segments of the backbone, through an unsaturated groupattached to the repeat unit, for example an acrylate group or a vinylgroup. The unsaturated group may be separated from the functional repeatunit by a spacer group. Polymers of this type are disclosed in, forexample, WO 96/20253.

In one embodiment, the hole transport polymer comprises a repeat unitcomprising general formula 25 or 26:

where Ar represents an aryl or heteroaryl group; x represents anoptional organic spacer group and R represents a polar substituentgroup.

where Ar represents an aryl or heteroaryl group; x represents anoptional organic spacer group and XY represents a group with a highdissociation constant, such that it effectively is ionised completely(X^(⊖)Y^(⊕))

In this embodiment the side groups comprising XY will be pendant from aconjugated region of the polymer backbone.

The spacer group x may be as defined anywhere herein. x may comprise agroup which breaks the conjugation between R (or XY) and Ar.

x may be substituted with more than one R (or XY) groups, for exampletwo R (or XY) groups.

Ar in formulae 25 to 28 may represent an aryl or heteroaryl groupdefined anywhere herein.

Ar in formulae 25 to 28 may represent biphenyl. A repeat unit comprisingformula 25 may comprise formula 29:

where R and x are as defined anywhere herein. Preferably R representsXY.

Preferably there is no spacer group x, giving formula 30 or 31:

where R is as defined anywhere herein. Preferably R represents XY.

Ar in formulae 25 to 28 may represent fluorene. A repeat unit comprisingformula 25 may comprise formula 32 or 33:

where x and R are as defined anywhere herein. Preferably R representsXY.

where x and R are as defined anywhere herein and R5 and R6 represent Hor a substituent group. Examples of substituents include solubilisinggroups such as C1-20 alkyl or alkoxy; electron withdrawing groups suchas fluorine, nitro or cyano; and substituents for increasing glasstransition temperature (Tg) of the polymer. Preferably R represents XY.

Preferably the spacer groups x are present in formulae 32 and 33.

A repeat unit having formula 25 may comprise one of formulae 2 to 6ashown above or formulae 34 to 40a:

where n2 is as defined above.

where R2 and n are as defined above.

where R2, R5, R6 and n′ are as defined above.

where R5 and R6 are as defined above.

where counterions X are as defined anywhere herein; n4 and n5 eachindependently is in the range of from 0 to 10, preferably 0 to 5; andeach R8 independently represents alkyl, preferably C1 to C10 alkyl, morepreferably methyl.

Ar in formulae 25 to 28 may represent phenyl. A repeat unit comprisingformula 25 may comprise formula 41:

where x and R are as defined anywhere herein and R1 represents H or asubstituent group. Examples of substituents include solubilising groupssuch as C1-20 alkyl or alkoxy; electron withdrawing groups such asfluorine, nitro or cyano; and substituents for increasing glasstransition temperature (Tg) of the polymer. Preferably R represents XY.

For example, a repeat unit comprising formula 25 may comprise formula42:

where R1 is as defined in relation to formula 41 and n is as definedabove.

A repeat unit comprising formula 25 may comprise formula 43:

where x and R are as defined anywhere herein. Preferably R representsXY.

For example, a repeat unit comprising formula 25 may comprise formula44:

Ar in formulae 25 to 28 may represent triphenylamine. A repeat unitcomprising formula 25 may comprise formula 45:

where x and R are as defined anywhere herein. Preferably R representsXY.

For example, a repeat unit comprising formula 25 may comprise formula46, 47 or 48:

where R7 represents H or a substituent group. Examples of substituentsinclude solubilising groups such as C1-20 alkyl or alkoxy; electronwithdrawing groups such as fluorine, nitro or cyano; and substituentsfor increasing glass transition temperature (Tg) of the polymer.

x in formula 45 may represent phenyl or biphenyl.

In addition to the repeat unit of formula 25, the polymer may containone or more further aryl or heteroaryl repeat units. This further repeatunit may be selected to tune the charge transporting and/or emissiveproperties further. For example, the polymer may comprise a triarylaminerepeat unit to aid hole transport.

The triarylamine repeat unit may be selected from formulae 7 to 12 asdefined above.

Desirably the hole transporting polymer may comprise a triarylaminerepeat unit and a fluorene repeat unit. The polymer may be an ABcopolymer.

The hole transport polymer as defined anywhere herein may comprise afluorene repeat unit comprising formula 50:

wherein R5 and R6 are independently selected from hydrogen or optionallysubstituted alkyl, alkoxy, aryl, arylalkyl, heteroaryl andheteroarylalkyl. More preferably, at least one of R5 and R6 comprises anoptionally substituted C4-C20 alkyl or aryl group. Most preferably, R5and R6 represent n-octyl.

The hole transport polymer may comprise a triarylamine repeat unit; afirst fluorene repeat unit of one of formulae 1 to 6b or 32 to 40a; andoptionally a second fluorene repeat unit as defined anywhere herein. Apreferred ratio of triarylamine repeat unit: first fluorene repeat unit:second fluorene repeat unit is 50:30:20.

The hole transport polymer may comprise a triarylamine repeat unit asdefined anywhere herein and a biphenyl repeat unit of one of formulae 29to 31.

The hole transport polymer may comprise fluorene repeat unit as definedanywhere herein and a phenyl repeat unit of one of formulae 41 to 44.

The hole transport polymer may comprise a linear polymer. Preferably atleast 5 mol % of the repeat units in the linear polymer are conjugatedalong the polymer backbone.

The hole transport polymer may have formula 51:

where R2 and n are as defined above.+

The hole transport polymer of formula 51 is derivable from a polymerhaving formula 52:

where n is as defined above.

The polymer having formula 52 may be prepared by copolymerising monomer(2):

The hole transport polymer may have formula 53:

The hole transport polymer having formula 53 may be prepared bycopolymerising monomer (4):

The hole transport polymer may have formula 54:

where R5 and R6 are as defined above in relation to formula 50.

The sulphonate containing monomer can be made according to the method inMacromolecules 1998, 31, 964-974, with appropriate modifications for theO(CH2)4SO3Na side groups in place of O(CH2)3SO3Na.

The hole transport polymer may comprise a dendrimer. A dendrimer is atree-like polymer, which comprises dendron(s) emanating from a centralcore. Usually there are at least three dendrons. A dendron comprises abranched unit. The branched unit may be a repeat unit in the dendron.Each dendron comprises a backbone. Side groups may be pendant from thebackbone.

The core of the dendrimer may comprise formula 55 or 56:

Each dendron may comprise a triarylamine repeat unit as defined anywhereherein. Each dendron may comprise a triarylamine repeat unit and afluorene repeat unit as defined anywhere herein. Each dendron maycomprise a thiophene repeat unit, optionally together with atriarylamine and/or fluorene repeat unit.

The nature and number of polar substituents are preferably selected suchthat the hole transport material is soluble in a solvent having adielectric constant at 20° C. of greater than 15, more preferably in therange 20-50. Dielectric constants of common solvents may be found in theCRC Handbook of Chemistry and Physics, 82nd Edition, page 8-127.

Examples of suitable polar solvents include water; C1-6 alcohols,preferably methanol, ethanol or propanol; dimethyl sulfoxide; anddimethylformamide. Further examples of polar solvents will be apparentto the skilled person. It is sufficient for the hole transport materialto be soluble in any one polar solvent so that the hole transportmaterial can be deposited from solution in the polar solvent.

Turning to the second layer and the second material, preferablematerials for the second material will depend upon the function of thelayer of the material in the device (for example semiconductive,emissive layer; charge transport layer; insulating layer etc.). Suitablematerials will be well-known to a person skilled in the art. Suitably,the second material is a polymer. However, the material is not solimited and can be, for example, a small molecule, dendrimer or a metalcomplex. Preferably, the second material is a light emissive material.

In the method according to the first aspect of the present invention,the second layer typically comprises the light emissive layer. As such,typically the emissive layer is deposited from a non-polar solvent.

Preferably, the second material comprises non-polar substituents forsolubilising the second material in a non-polar solvent. Preferrednon-polar substituents include C1-20 alkyl and alkoxy groups.

The non-polar solvent preferably is a common organic solvent. Preferrednon-polar solvents are those having a dielectric constant at 20° C. ofless than 10, more preferably less than 5, most preferably less than 3.Examples of such solvents are benzene and mono- or polyalkylatedbenzene, in particular xylene and toluene.

Suitable techniques for solution processing the hole transport materialand the second material will be well known to those skilled in this art.Preferred techniques include ink-jet printing and spin coating and rollprinting.

Other materials can be present with the hole transport material in thesolution. In this regard, it may be necessary to control the processingproperties of all of the materials in the solution by introducing polarsubstituent groups.

In the method according to the first aspect of the present invention,the electronic device preferably comprises a light-emitting device(LED).

Where the device is an LED, the LED will have an anode, a cathode and alight emissive layer located between the anode and the cathode. Theanode may be, for example, a layer of transparent indium tin oxide. Thecathode may be, for example, LiAl. Holes and electrons that are injectedinto the device recombine radiatively in the light emissive layer. Thehole transport layer is located between the anode and the light emissivelayer. Optionally, a hole injection layer, such as a layer ofpolyethylene dioxythiophene (PEDT), may be present between the holetransport layer and the anode. This provides an energy level which helpsthe holes injected from the anode to reach the hole transport layer andthe light emissive layer.

The LED also may have an electron transport layer situated between thecathode and a light emissive layer. This provides an energy level whichhelps the electrons injected from the cathode to reach the lightemissive layer.

The light emissive layer can itself comprise a laminate, effectivelymade up of sub-layers.

The LED may have further layers in addition to those mentioned above.For example, the LED may have one or more charge or exciton blockinglayers.

In one embodiment of the method according to the first aspect of thepresent invention, the hole transport material comprises a holetransport polymer as defined anywhere herein and the second materialcomprises a second polymer. The hole transport polymer may comprise arepeat unit comprising an aryl or heteroaryl group. The second polymermay comprise a repeat unit comprising an aryl or heteroaryl group, whichis the same as the aryl or heteroaryl group comprised in the repeat unitof the hole transport polymer. The aryl group or heteroaryl group can bedifferently substituted however in the hole transport polymer ascompared with the second polymer. Preferred aryl and heteroaryl groupsare as discussed above.

The method according to the first aspect of the present invention maycomprise the further step of forming a third layer of the device. Itwill be understood that advantageously, the step of forming the thirdlayer can be carried out whilst the second material remains soluble inthe second solvent. Thus, there is no need to crosslink the secondmaterial after deposition.

The third layer of the device can be formed by depositing over thesecond material a third material from solution in a third solvent inwhich the second layer is substantially insoluble. The third solvent isa polar solvent, which may be the same or different as the polar solventused to deposit the hole transport layer. Polar substituent groups arepresent on the third material so that the third material is soluble inthe polar solvent. The second layer is substantially insoluble in thepolar solvent used to deposit the third material. Preferred polarsubstituent groups for the third material are as discussed above inrelation to the hole transport material.

Knowing the function of the second layer in the device, the skilledperson will know a desirable function for the third layer and thus willknow suitable materials for selection as the third material. The thirdmaterial preferably comprises a polymer. However, the material is not solimited and can be, for example, a small molecule, dendrimer or a metalcomplex. Preferably, the third layer is a polar electron transportlayer.

The first aspect of the present invention further provides asemiconductive hole transport material containing polar substituentgroups, the hole transport material being soluble in a polar solvent.The hole transport material may be as defined anywhere above in relationto the first aspect of the present invention.

The first aspect of the present invention still further provides the useof the aforementioned semiconductive hole transport material in a methodfor forming an organic electronic device. The first aspect still furtherprovides an organic electronic device containing a hole transport layer,the hole transport layer comprising the aforementioned semiconductivehole transport material for transporting holes in the device.

The first aspect of the present invention further provides an organicelectronic device obtained or obtainable by the method according to thefirst aspect of the present invention. The device includes a holetransport layer comprising a hole transport material, said holetransport material containing polar substituent groups selected so thatthe hole transport material is soluble in a polar solvent. Preferredfeatures of the device are as discussed anywhere above in relation tothe method according to the first aspect of the present invention.

Finally, the first aspect of the present invention provides a method ofmanufacturing a semiconductive hole transport polymer containing polarsubstituent groups, the polymer being as described anywhere above inrelation to the first aspect of the present invention. The holetransport polymer may first be prepared in precursor form.

Preferred methods for preparation of the semiconductive hole transportpolymer are Suzuki polymerisation as described in, for example, WO00/53656 and Yamamoto polymerisation as described in, for example, T.Yamamoto, “Electrically Conducting And Thermally Stable π-ConjugatedPoly(arylene)s Prepared by Organometallic Processes”, Progress inPolymer Science 1993, 17, 1153-1205. These polymerisation techniquesboth operate via a “metal insertion” wherein the metal atom of a metalcomplex catalyst is inserted between an aryl group and a leaving groupof a monomer. In the case of Yamamoto polymerisation, a nickel complexcatalyst is used; in the case of Suzuki polymerisation, a palladiumcomplex catalyst is used.

For example, in the synthesis of a linear polymer by Yamamotopolymerisation, a monomer having two reactive halogen groups is used.Similarly, according to the method of Suzuki polymerisation, at leastone reactive group is a boron derivative group such as a boronic acid orboronic ester and the other reactive group is a halogen. Preferredhalogens are chlorine, bromine and iodine, most preferably bromine.

It will therefore be appreciated that repeat units and end groupscomprising aryl groups as illustrated throughout this application may bederived from a monomer carrying a suitable leaving group(s).

Suzuki polymerisation may be used to prepare regioregular, block andrandom copolymers. In particular, homopolymers or random copolymers maybe prepared when one reactive group is a halogen and the other reactivegroup is a boron derivative group. Alternatively, block or regioregular,in particular AB, copolymers may be prepared when both reactive groupsof a first monomer are boron and both reactive groups of a secondmonomer are halogen.

As alternatives to halides, other leaving groups capable ofparticipating in metal insertion include tosylate, mesylate, phenylsulfonate and triflate.

Monomers for preparing a polymer according to the method of the secondaspect may comprise formula 57 or 58:

where Ar, x, and R are as defined anywhere above; L and L′ are reactivegroups suitable for participating in a polymerisation reaction; and (R)represents a precursor to R, which may be converted to R afterpolymerisation. Preferably R represents XY.

L and L′ may represent Br.

Preferred monomers include those comprising the structure shown in oneof formulae 59 to 83:

In any of the above formulae 59 to 83, R may be replaced by (R) asdefined in relation to formula 58.

Polymers with a part or the whole of the backbone being non-conjugatedmay be formed by polymerising the repeat units, which formnon-conjugated segments of the backbone, through an unsaturated groupattached to the repeat unit, for example an acrylate group or a vinylgroup. The unsaturated group may be separated from the functional repeatunit by a spacer group. Polymers of this type are disclosed in, forexample, WO 96/20253.

Turning to the second aspect of the present invention, since the presentinvention provides a means for controlling the processing of materials,it is not necessary to select materials for use in the electronic devicewithin the confines of those materials already having suitableprocessing properties. The disadvantages of having to select materialsfor use in the electronic device within the confines of those materialsalready having suitable processing properties have been discussed abovewith reference to the prior art. The present invention enablesmaterials, which by design are soluble in polar solvents. Where thedevice contains a multilayer of polymers this leads to greaterflexibility in the range of repeat units that can be used in the variouspolymers. For example, for adjacent polymer layers A and B in a deviceit is possible to select both polymer A and polymer B to contain arepeat unit comprising the same aryl or heteroaryl group. Polymer A andpolymer B can both comprise a fluorene or triarylamine repeat unit forexample. The processing properties of either polymer A or polymer B canbe modified using polar substituent groups so that the polymers havedifferent solubility behaviour.

Thus, in accordance with the second aspect, the present invention isapplied in the case where two materials that are to be deposited inadjacent layers of an electronic device have similar structures (e.g.polymers having the same or similar repeat units in the backbone). Thepresent invention allows the processing properties of one or other ofthe materials to be controlled so that they are not soluble in the samesolvents. Thus, the second aspect provides a method for forming anorganic electronic device, including the steps of:

depositing a first polymer from solution in a first solvent to form afirst layer of the device; and subsequently

forming a second layer of the device by depositing a second polymer fromsolution in which the first layer is substantially insoluble; where thesolution containing the second polymer comprises a second solvent, andeither the first solvent or the second solvent is a polar solvent; andwhere the first polymer or the second polymer contains polar substituentgroups selected so that the first polymer or the second polymer issoluble in the polar solvent, the other of the first polymer and thesecond polymer being substantially insoluble in the polar solvent; andcharacterised in that the first polymer comprises a repeat unit Ar1 andthe second polymer comprises a repeat unit Ar2. Ar1 and Ar2 comprise thesame aryl or heteroaryl group, although the aryl or heteroaryl group maybe differently substituted in Ar1 as compared with Ar2. In other words,Ar1 and Ar2 comprise a common aryl or heteroaryl group.

For optimising solution processing, particularly ink jet printing, amixture of solvents may be present in the afore-mentioned solutions.

It will be understood that advantageously, the step of forming thesecond layer can be carried out whilst the first polymer remains solublein the first solvent. Thus, there is no need to crosslink the firstpolymer after deposition.

The polar substituent groups are covalently attached to the first orsecond polymer.

Preferred aryl and heteroaryl groups include fluorene, phenylene,phenylenevinylene, benzothiadiazole, thiophene, triarylamine,indenofluorene, and spirofluorene groups. A particularly preferred arylor heteroaryl group for the method according to the second aspect isfluorene.

In the second aspect of the present invention, preferably, the firstlayer is a hole transport layer. Further, preferably, the second layeris a light emissive layer and/or an electron transport layer.

In one embodiment of this preferred arrangement, the first polymer is ahole transporting polymer comprising polar substituent groups asdiscussed above in respect of the first aspect of the invention, and thesecond polymer is a light-emissive polymer deposited from a non-polarsolvent solution. In some cases, neutral polar substituent groups mayrender the first polymer soluble in polar solvents without rendering itsubstantially insoluble in non-polar solvents. It is therefore preferredthat the hole transporting polymer according to this embodiment isrendered substantially insoluble in the non-polar solvent bysubstitution with a charged polar substituent groups.

In another embodiment of this preferred arrangement, the first polymeris a hole transporting polymer that is substantially insoluble in polarsolvents, and the second polymer is a light-emissive polymer depositedfrom a polar solvent solution. In this embodiment, it is preferred thatthe light-emissive polymer is rendered soluble in the polar solvent bysubstitution with neutral polar substituent groups because the presenceof dissociating groups in the emissive layer as described for thecharged polar substituents described above may result in doping of theemissive layer to the detriment of device performance.

The preferred number and nature of polar substituent groups contained inthe first polymer or the second polymer are as discussed above inrelation to the first aspect of the present invention with the provisothat it is not essential in the second aspect for the polymer containingpolar substituent groups to be a hole transport polymer.

Preferably, whichever of the first polymer and the second polymer issubstantially insoluble in the polar solvent comprises non-polarsubstituents for solubilising the material in a non-polar solvent.

Suitable techniques for solution processing the first polymer and thesecond polymer will be well known to those skilled in this art.Preferred techniques include ink-jet printing and spincoating.

Whichever of the first polymer and the second polymer is substantiallyinsoluble in the polar solvent, preferably is deposited from solution ina non-polar solvent, more preferably a common organic solvent.

Preferable polymers for the first polymer and the second polymer willdepend upon the function of the layer of the polymer in the device (forexample emissive layer; charge transport layer; insulating layer etc.).

Referring to the polymer containing polar substituent groups, thepolymer preferably is conjugated. The polymer preferably is partially orfully conjugated along the polymer backbone. It is preferred that thereis a break in the conjugation between each polar substituent group andthe conjugated segment or segments of the polymer. This helps tominimise the effect of the polar substituent groups on the electronicproperties of the polymer. To this end, a spacer group may be introducedbetween a polar substituent group and the conjugated segment or segmentsof the polymer. Suitable spacer groups (x and x′) comprise saturatedhydrocarbyls, such as (CH2)n where n is in the range of from 1 to 5,preferably in the range of 1 to 3.

In one embodiment, a conjugated spacer group is preferable, for examplea spacer group comprising an aryl or heteroaryl group, such as phenyl.In this embodiment, each aryl or heteroaryl group can carry one or more(for example two) polar substituent groups.

In one embodiment it is preferred that at least one of x and x′comprises at least one substituted or unsubstituted aryl or heteroarylgroup. In this regard, reference is made to WO 02/092723. In oneembodiment it is preferred for the proportion of polar substituentgroups to be present as substituents on the aryl or heteroaryl groups atthe 9 position of the fluorene repeat units described in WO 02/092723.Examples of preferred fluorene-containing polymers are provided above inrelation to the first aspect of the present invention with the provisothat it is not essential in the second aspect for the polymer containingpolar substituent groups to be a hole transport polymer.

Other preferred repeat units to be present in the first polymer and/orthe second polymer in the second aspect of the present invention arethose comprising a group selected from a p-linked dialkyl phenylene, ap-linked disubstituted phenylene, a phenylene vinylene, a 2,5-linkedbenzothiadiazole, a 2,5-linked substituted benzothiadiazole, a2,5-linked disubstituted benzothiadiazole, a 2,5-linked substituted orunsubstituted thiophene or a triarylamine.

Typically, the polymer whose processing properties are controlled by themethod of the second aspect of the present invention is soluble incommon organic solvents in the absence of the proportion of polarsubstituents.

The method according to the second aspect of the present invention maycomprise the further step of forming a third layer of the device. Thethird layer of the device can be formed by depositing over the secondpolymer a third material from solution in a third solvent in which thesecond layer is substantially insoluble.

It will be understood that advantageously, the step of forming the thirdlayer can be carried out whilst the second polymer remains soluble inthe second solvent. Thus, there is no need to crosslink the secondpolymer after deposition.

The third solvent may or may not be a polar solvent. If the firstsolvent is a polar solvent then the third solvent also will be a polarsolvent, which may be the same as or different from the first solvent.Where the third solvent is a polar solvent, polar substituent groups arepresent on the third material so that the third material is soluble inthe polar solvent. Preferred polar substituent groups for the thirdmaterial are as discussed above.

Knowing the function of the first and second layers in the device, theskilled person will know a desirable function for the third layer andthus will know suitable materials for selection as the third material.The third material preferably comprises a polymer.

However, the third material is not so limited and can be for example asmall molecule, dendrimer or a metal complex. Preferably, the firstlayer is a polar hole transport layer, the second layer is a non polaremissive layer, and the third layer is a polar electron transport layer.

The second aspect of the present invention further provides an organicelectronic device obtained or obtainable by the method according to thesecond aspect of the present invention. Preferred features of the deviceare as discussed anywhere above in relation to the first aspect of thepresent invention with the proviso that it is not essential in thesecond aspect for the polymer containing polar substituent groups to bea hole transport polymer or indeed for the device to contain a holetransport layer.

Development of the present invention as discussed above has led to athird aspect of the invention. The third aspect of the invention isdiscussed below.

The present inventors have discovered that when a hole transportmaterial contains polar substituent groups (as discussed in relation tothe method according to the first aspect) then under certain conditionsit is possible for the next layer of the device to be deposited fromsolution in a solvent in which the hole transport layer is otherwisesoluble, without destroying the integrity of the hole transport layer.The present inventors have observed this effect when the hole transportmaterial is deposited onto a layer of conducting material containingpolar groups (e.g. PEDT/PSS).

The present inventors have found that interaction between the polarsubstituents in the hole transport material and the polar groups in theconducting material stabilises the hole transport layer thus formed. Infact, the present inventors have found that this interaction allows thesubsequent (typically emissive) layer to be deposited from solution inwhich the hole transporting polymer would otherwise dissolve. In otherwords, the hole transport material and subsequent layer material neednot have different solubilities in a given solvent.

Therefore, a third aspect of the present invention provides a method forforming an organic electronic device, including the steps of:

forming a conducting layer comprising a conducting material, saidconducting material containing polar groups; and

forming a hole transport layer comprising a semiconductive holetransport material on the conducting layer, characterised in that saidhole transport material contains polar substituent groups.

In the method according to the third aspect, should it be desirable, thenext (third) layer of the device, which is formed on the hole transportlayer, can be deposited by processing from solution in a solvent inwhich the hole transport layer is soluble in the absence of theconducting layer. Alternatively, the next layer of the device may beformed on the hole transport layer in accordance with the methodaccording to the first aspect of the present invention. The third layercomprises a third material. Suitable materials for the third layer areas defined above in relation to the second material discussed inrelation to the first aspect of the present invention.

It will be understood that, typically, the hole transport material willcontain polar substituent groups selected so that the hole transportmaterial is soluble in a polar solvent. In this regard, preferred holetransport materials are as discussed above in relation to the firstaspect of the present invention.

Any suitable conducting material containing polar groups can be usedprovided that a stabilising interaction is formed between the layer ofthe conducting material and the hole transport layer. Preferably, theconducting material comprises an organic conducting material. Thepresence of a stabilising interaction can be determined by testingwhether the stabilised hole transport layer is substantially insolublein a solvent in which it would otherwise be soluble. In fact, it hasbeen discovered that in some cases a stabilising interaction can beformed even when the hole transport material does not contain polarsubstituent groups. Therefore, the third aspect of the present inventionfurther provides a method for forming an organic electronic device,including the steps of:

forming a conducting layer comprising a conducting material; and

forming a hole transport layer on the conducting layer by depositing asolution comprising a semiconductive hole transport material,characterised in that said hole transport material irreversibly binds tosaid conducting material to render the hole transport layer insolublewithout substantially affecting the electronic properties of the holetransport material.

For optimising solution processing, particularly ink jet printing, amixture of solvents may be present in the afore-mentioned solutions.

The hole transport material may be deposited from solution in anon-polar solvent. Alternatively, as discussed above, the hole transportmaterial may be deposited from solution in a polar solvent.

In the context of the third aspect of the present invention, it will beunderstood that the hole transport layer is rendered insoluble insofaras it is possible to deposit a solution of the next layer of the deviceon the hole transport layer, in which solution the hole transportmaterial might otherwise be soluble in the absence of the bindinginteraction between the hole transport material and the conductingmaterial. The irreversible binding interaction means that all of thehole transport layer can not be washed off using the same solvent thatwas used to deposit the hole transport material, even under forcingconditions, for example continuous washing until the thickness of thelayer remains constant even with further washing. This allows the nextlayer of the device to be deposited without substantially affecting theintegrity of the hole transport layer.

Preferably, an at least 10 nm thickness of hole transport layer remainsafter continuous washing.

Typically, the hole transport material comprises a hole transportpolymer. In this case, preferably, side chains or side groups pendantfrom the backbone of the hole transport polymer form the stabilising,irreversible binding interaction with the conducting material. This hasthe benefit of decoupling the effects that the interaction could have onthe electronic properties of the polymer. Preferably, the side chains orside groups which form the stabilising, irreversible binding interactionwith the conducting material are not in conjugation with the polymerbackbone.

In one embodiment no repeat unit in the backbone of the hole transportpolymer irreversibly binds to the conducting material.

In one embodiment the hole transport polymer is not PVK. In oneembodiment the hole transport polymer does not contain a fluorene repeatunit in the polymer backbone.

The nature of the stabilising, irreversible binding interaction may varyfrom system to system. Stabilising interactions that are capable ofrendering the hole transport layer insoluble include protonation of thehole transport material by the conducting material; hydrogen bondsformed between the hole transporting material and the conductingmaterial; and dipolar interactions between the hole transport materialand the conducting material.

The hole transport material may contain polar substituent groups, asdiscussed above in relation to the first aspect of the invention.

The hole transport material may contain O or N. Preferably, the O or Natoms accept protons from the conducting material to form theirreversible binding interaction. In particular, the hole transportmaterial may contain amine or morpholine groups, which may be protonatedby a conducting material such as PEDT doped with a charge balancingdopant. The charge balancing dopant may be acidic. The charge balancingdopant may be a polyanion. Preferably the charge balancing dopantcomprises a sulfonate, such as poly(styrene sulfonate) (PSS) where thePEDT conducting polymer is blended with acidic polar PSS groups. Whenthe hole transport material comprises a hole transport polymer, thegroups that are protonated by the conducting material preferably arependant from the polymer backbone.

Generally, the stabilising, irreversible binding interaction between thehole transport material and the conducting material occurs spontaneouslyduring deposition of the hole transport material on the conductinglayer. However, the possibility of treating the hole transport layerafter deposition is not excluded.

It may also be desirable to control the contact time between thesolution comprising the semiconductive hole transport material and theconducting layer.

Of course, the electronic properties of the conducting material must becompatible with device performance, i.e. the conducting material shouldbe capable of transporting holes from the anode to the hole transportlayer.

The conducting material may contain polar groups.

Preferably, the conducting material comprises a conducting polymer.

The conducting material may comprise an organic conducting material suchas a hole injecting material.

One particularly preferred organic conducting material comprises a holeinjecting material, such as poly(ethylene dioxythiophene) (PEDT) dopedwith a charge balancing dopant. The charge balancing dopant may beacidic. The charge balancing dopant may be a polyanion. Preferably thecharge balancing dopant comprises a sulfonate, such as poly(styrenesulfonate) (PSS) where the PEDT conducting polymer is blended withacidic polar PSS groups.

An excess of the material comprising the charge balancing dopant may bepresent. It will be understood that any excess of the materialcomprising the charge balancing dopant will not be performing thefunction of doping and, so, will be present in a neutral form, forexample as a salt or an acid. The excess of the material comprising thecharge balancing dopant may be present as a charged species togetherwith one or more counterions. These counterions may interact with thehole transport material to form the irreversible binding interaction.Preferably, the excess of the material comprising the charge balancingdopant comprises sulfonic acid groups or a salt thereof.

Polar substituent groups on the hole transporting material may interactwith the polar groups in the poly(styrene sulfonate) by irreversiblybinding thereto, thereby stabilising the hole transport layer that isformed.

Another preferred hole injecting material is polyaniline formulated withsulphonic acid.

The method according to the third aspect may include a further step offorming a further layer of the device on the hole transport layer bydepositing an electroactive material in a suitable solvent on the holetransport layer. The further layer may be the emissive layer.

The method according to the third aspect may include a further step ofheating the hole transport layer. Alternatively, the method maypositively exclude such a step.

The thickness of the hole transport layer may be from 10 to 50 nm.

It will be understood that in the method according to the third aspectof the present invention, the hole transport layer is formed bydepositing a solution comprising hole transport material. In oneembodiment, the solution consists of the hole transport materialdissolved in a suitable solvent or mixture of solvents.

In another embodiment of the third aspect of the present invention, thesolution comprises a hole transport material together with at least oneother electroactive material in a suitable solvent or mixture ofsolvents. The other electroactive material may be selected from anemissive material or a charge transport material, for example. Byappropriate selection of the other electroactive material, it has beenfound that after deposition, the hole transport material and the otherelectroactive material may phase separate to form two layers of thedevice; the hole transport material phase separating to form the holetransport layer on the conducting layer and the at least one otherelectroactive material forming a further electroactive layer on the holetransport layer.

In the embodiment where the hole transport material is depositedtogether with another electroactive material in a suitable solvent andthen allowed to phase separate after deposition, it will be understoodthat there is no advantage (with respect to forming the next layer ofthe device) in the hole transport material being rendered insoluble and,thus, it is not essential for the hole transport material toirreversibly bind to the conducting material.

Therefore, the third aspect of the present invention further provides amethod for forming an organic electronic device, including the steps of:

forming a conducting layer comprising a conducting material; and

forming a hole transport layer on the conducting layer by depositing asolution comprising a semiconductive hole transport material togetherwith at least one other electroactive material directly onto theconducting layer, characterised in that the hole transport materialphase separates from the at least one other electroactive material afterdeposition to form the hole transport layer comprising thesemiconductive hole transport material on the conducting layer whereinone of the semiconductive hole transport material at the at least oneother electroactive material contains a polar substituent group.

It will be understood that the at least one other electroactive materialtherefore forms an electroactive layer on the hole transport layer.

For optimising solution processing, particularly ink jet printing, amixture of solvents may be present in the afore-mentioned solution.

It will be appreciated that it is necessary in this embodiment for thehole transport material and the at least one other electroactivematerial to be soluble in a common solvent. Preferably, a non-polarsolvent is used and it is therefore preferred that the polar substituentgroup is a neutral polar substituent group present in sufficiently lowconcentration to solubilise the material it is bound to in a polarsolvent without rendering this material insoluble in non-polar solvents.In contrast, a charged polar substituent group is likely to render thematerial insoluble in non-polar solvents even at relatively lowconcentrations.

It will be understood that in order to achieve phase separation, thehole transport material should have an affinity for the conductingmaterial and the at least one other electroactive material should haveno affinity or a weaker affinity for the conducting material. To thisend, when the conducting material contains an acid, the hole transportmaterial preferably contains polar substituent groups and the polarsubstituent groups preferably react with the conducting material to formthe conjugate base of the acid.

The conducting material may comprise an organic conducting material, forexample an organic hole injecting material as defined anywhere herein.

It has been found that, in one embodiment, the hole transport materialhas an affinity for the conducting material when the conducting materialcontains polar groups, as described anywhere herein, and the holetransport material contains polar substituent groups, as describedanywhere herein. Particularly, the hole transport material may be asdefined anywhere in relation to the first aspect of the invention.

The affinity may be optimised by selection of the number and location ofthe polar groups in the conducting material and the number and locationof the polar substituent groups in the hole transport material. In thisregard, when the hole transport material comprises a polymer, it isdesirable for side chains or side groups pendant from the polymerbackbone to comprise the polar substituent groups. Preferably, the sidechains or side groups are not in conjugation with the polymer backbone.In this embodiment, the conducting material preferably comprises anorganic conducting material, more preferably an organic conductingpolymer, more preferably PEDT doped with a suitable charge balancingdopant. The charge balancing dopant may be acidic. The charge balancingdopant may be a polyanion. Preferably the charge balancing dopantcomprises a sulfonate, such as poly(styrene sulfonate) (PSS) where thePEDT conducting polymer is blended with acidic polar PSS groups.

The hole transporting material preferably comprises alkyl aminesubstituent groups, such as morpholine substituent groups, as discussedabove.

In another embodiment, the surface of the conducting layer is treatedprior to deposition of the solution comprising the hole transportmaterial and the further electroactive material in order to render thesurface of the conducting layer hydrophobic such that deposition of apolymer blend according to the third aspect of the invention will phaseseparate with the non-polar material at the conducting layer surface. Bythis technique, a phase separated blend may be formed using a non-polarhole transporting material and an electroactive material comprising apolar substituent, for example morpholine. Any suitable known surfacetreatment may be used, for example treatment with chlorosilanes.

Preferably, the at least one other electroactive material comprises anelectroactive polymer. More preferably, the at least one otherelectroactive material comprises an emissive material, particularly anemissive polymer.

When phase separation occurs, it is possible to form the hole transportlayer and a further electroactive layer of the device (for example theemissive layer) in a one step process.

In one embodiment, the hole transport layer also may function as anemissive layer in the device, the hole transport material functioning totransport holes to the electroactive layer situated thereon and also toemit light. In this embodiment, the hole transport layer may beconsidered as a first emissive layer and the electroactive layersituated thereon preferably is a second emissive layer of the device.Preferably, the colour of the combined emission seen from the first andsecond emissive layers is white. To this end, preferably the holetransport layer (first emissive layer) emits blue light and the secondemissive layer emits light of a longer wavelength. The blue light incombination with the longer wavelength light achieves white lightemission from the device. Preferably, the hole transport layer (firstemissive layer) emits blue light and the second emissive layer emitsyellow light.

The “white light” may be characterised by a CIE x coordinate equivalentto that emitted by a black body at 3000-9000K and CIE y coordinatewithin 0.05 of the CIE y co-ordinate of said light emitted by a blackbody.

The “blue light” may be characterised by a CIE x co-ordinate less thanor equal to 0.25, more preferably less than or equal to 0.2, and a CIE yco-ordinate less than or equal to 0.3, more preferably less than orequal to 0.2.

Yellow light may be characterised by CIE coordinates in the range x>0.3,y>0.3.

In this embodiment, the hole transport material may be any suitablematerial, particularly any material described herein, provided that itis capable of emitting light, preferably blue light. A preferred bluelight emitting, hole transporting polymer has formula 100:

(100)

Any suitable emissive material may be used as the electroactive polymerin the second emissive layer.

The third aspect of the present invention further provides an organicelectronic device obtained or obtainable by one of the method accordingto the third aspect of the present invention. Preferred features of thedevice are as discussed anywhere above in relation to the first aspectof the present invention.

In a fourth aspect, the present invention provides a method for formingan organic electronic device, including the steps of:

forming a conducting layer comprising a conducting material; and

forming a hole transport layer over the conducting layer by depositing asemiconductive hole transport material from solution in a non-polarsolvent, the hole transport layer being substantially insoluble in apolar solvent; and

forming an emissive layer on the hole transport layer by depositing anemissive material from a solution in the polar solvent wherein theemissive material contains a neutral polar substituent group.

For optimising solution processing, particularly ink jet printing, amixture of solvents may be present in the afore-mentioned solutions.

The conducting material may be as described anywhere herein.

The polar substituent groups are covalently attached to the emissivematerial. In the absence of the polar substituent groups, the emissivematerial still is capable of emission. Thus, the polar substituentgroups substantially do not affect the electronic properties of theemissive material.

Preferred neutral polar substituent groups are as discussed in the firstaspect of the invention. The use of neutral polar substituent groupsavoids the possibility of device performance being adversely affected bydoping of the emissive material that may be caused by dissociatinggroups charged polar substituent groups.

Turning to the fifth aspect of the present invention, it will beunderstood from the discussion above relating to the first, second,third and fourth aspects of the present invention, that some of thematerials used in the methods of the invention are novel. Therefore, thefifth aspect of the present invention provides novel materials asdescribed above in relation to the first, second, third and fourthaspects of the present invention. In particular, the fifth aspect of thepresent invention provides a polymer suitable for use in an organicelectronic device, said polymer comprising a repeat unit comprising anaryl or heteroaryl group, characterised in that the polymer comprisesoptionally substituted units of formula (84) pendant from the polymerbackbone:

wherein Z is selected from the group consisting of O, S or NR′″ and R′″is H or a substituent.

Where Z is NR′″, R′″ may be a polar or non-polar substituent. Preferredpolar substituents R′″ include amino groups, preferably trialkylaminogroups; polar heterocyclic groups, for example pyridine; and ether andpolyether groups. Preferred non-polar substituents R′″ include C1-20hydrocarbyl.

Preferably, Z=O, i.e. the unit of formula (84) is optionally substitutedmorpholine.

Preferably, the aforementioned aryl or heteroaryl group is in thepolymer backbone.

The units of formula 84 may be spaced from the polymer backbone byspacer groups as discussed above in relation to the first aspect of thepresent invention. When present, preferred spacer groups include phenyland alkyl chains such as (CH2)₆.

It is preferred that there is a break in conjugation between the unitsof formula 84 and the polymer backbone.

The polymer may be a hole transport polymer, electron transport polymeror emissive polymer, for example.

Preferably, the polymer according to the fifth aspect is partially orfully conjugated along the polymer backbone.

Preferred aryl and heteroaryl groups are as discussed above in relationto the first aspect of the present invention. It is particularlypreferred that the morpholine groups are pendant from fluorene groups inthe polymer backbone, as shown below in formula 85 for example:

Where x and x′ are optional spacer groups as defined anywhere herein; n4and n5 each independently is in the range of from 0 to 5; n6 is 1 or 2;and n7 is 1 or 2.

The polymer according to the fifth aspect may comprise a copolymer.Suitable co-repeat units to be present in the copolymer include fluorenerepeat units; and triarylamines, such as those having formulae 7 to 12defined above.

In another embodiment, the fifth aspect of the present inventionprovides a semiconductive hole transport material containing polarsubstituent groups, the polar substituent groups substantially notaffecting the electronic properties of the hole transport material andthe hole transport material being soluble in a polar solvent.Preferably, the hole transport material has a pH less than or equal to3. Other preferred features of the material are as discussed aboveanywhere in relation to the first, second, third or fourth aspects ofthe invention.

In still another embodiment, the fifth aspect of the present inventionprovides a material comprising a semiconductive hole transport materialand one or more functional groups covalently attached to thesemiconductive hole transport material, each functional group comprisinga substituent, the or each functional group not being in conjugationwith the semiconductive hole transport material and the substituent(s)rendering the material soluble in a polar solvent. The presence of thefunctional group(s) substantially does not affect the electronicproperties of the semiconductive hole transport material because itis/they are not in conjugation with the semiconductive hole transportmaterial.

The substituent may comprise a polar substituent group as definedanywhere herein. The hole transport material may be as discussedanywhere in relation to the first aspect of the present invention.

Preferably, the hole transport material comprises a hole transportpolymer, the functional group being comprised in a side chain or sidegroup pendant from the backbone of the polymer.

When the functional groups are comprised in a side chain or side grouppendant from the backbone of the polymer, the functional groups may belinked to the polymer backbone by spacer groups, for example asdescribed anywhere herein. Preferred spacer groups provide a break inconjugation between the functional group and the polymer backbone. Morepreferred spacer groups include saturated hydrocarbyls.

Preferably, the hole transport material contains a plurality offunctional groups.

A sixth aspect of the present invention provides a method for forming anorganic electronic device, including the steps of:

forming a conducting layer comprising a conducting material; and

forming a hole transport layer on the conducting layer by depositing asolution comprising a semiconductive hole transport material,characterised in that said hole transport material contains substituentgroups that bind to said conducting material to render the holetransport layer insoluble without substantially affecting the electronicproperties of the hole transport material.

For optimising solution processing, particularly ink jet printing, amixture of solvents may be present in the afore-mentioned solution.

The hole transport material may be deposited from solution in anon-polar solvent. Alternatively, as discussed above, the hole transportmaterial may be deposited from solution in a polar solvent.

In the context of the sixth aspect of the present invention, it will beunderstood that the hole transport layer is rendered insoluble insofaras it is possible to deposit a solution of the next layer of the deviceon the hole transport layer, in which solution the hole transportmaterial might otherwise be soluble in the absence of the bindinginteraction between the hole transport material and the conductingmaterial.

Typically, the hole transport material according to the sixth aspectcomprises a hole transport polymer. In this case, preferably, sidechains or side groups pendant from the backbone of the hole transportpolymer comprise the substituents that bind to the conducting material.This has the benefit of decoupling the effects that the interactioncould have on the electronic properties of the polymer. Preferably, thesubstituents which bind to the conducting material are not inconjugation with the polymer backbone.

The nature of the binding may vary from system to system. Bindingmechanisms include protonation of the hole transport material by theconducting material; hydrogen bonds formed between the hole transportingmaterial and the conducting material; and dipolar interactions betweenthe hole transport material and the conducting material. Preferably, thesubstituents accept protons from the conducting material to generatebinding.

The substituents may comprise polar substituent groups, as discussedabove in relation to the first aspect of the invention. Preferably, thesubstituents contain O or N and more preferably, the O or N atoms acceptprotons from the conducting material to generate binding. The holetransport material may be as discussed anywhere in relation to the firstaspect of the present invention.

Generally, the binding between the hole transport material and theconducting material according to the sixth aspect occurs spontaneouslyduring deposition of the hole transport material on the conductinglayer. However, the possibility of treating the hole transport layerafter deposition is not excluded.

It may also be desirable to control the contact time between thesolution comprising the semiconductive hole transport material and theconducting layer.

Of course, the electronic properties of the conducting material must becompatible with device performance, i.e. the conducting material shouldbe capable of transporting holes from the anode to the hole transportlayer.

The conducting material may contain polar groups.

Preferably, the conducting material comprises a conducting polymer.

The conducting material may comprise an organic conducting material,such as a hole injecting material.

One particularly preferred organic conducting material comprises a holeinjecting material, such as poly(ethylene dioxythiophene) (PEDT) dopedwith a charge balancing dopant. The charge balancing dopant may beacidic. The charge balancing dopant may be a polyanion. Preferably thecharge balancing dopant comprises a sulfonate, such as poly(styrenesulfonate) (PSS) where the PEDT conducting polymer is blended withacidic polar PSS groups.

An excess of the material comprising the charge balancing dopant may bepresent. It will be understood that any excess of the materialcomprising the charge balancing dopant will not be performing thefunction of doping and, so, will be present in a neutral form, forexample as a salt or an acid. The excess of the material comprising thecharge balancing dopant may be present as a charged species togetherwith one or more counterions. These counterions may interact with thehole transport material to form the irreversible binding interaction.Preferably, the excess of the material comprising the charge balancingdopant comprises sulfonic acid groups or a salt thereof.

The hole transport material may be protonated by a conducting materialsuch as PEDT doped with PSS.

Another preferred hole injecting material is polyaniline formulated withsulphonic acid.

The method according to the sixth aspect may include a further step offorming a further layer of the device on the hole transport layer bydepositing an electroactive material in a suitable solvent on the holetransport layer. The further layer may be the emissive layer.

The method according to the sixth aspect may include a further step ofheating the hole transport layer. Alternatively, the method maypositively exclude such a step.

The thickness of the hole transport layer may be from 10 to 50 nm.

It will be understood that in the method according to the sixth aspectof the present invention, the hole transport layer is formed bydepositing a solution comprising hole transport material. In oneembodiment, the solution consists of the hole transport materialdissolved in a suitable solvent or mixture of solvents.

In another embodiment of the sixth aspect of the present invention, thesolution comprises a hole transport material together with at least oneother electroactive material in a suitable solvent or mixture ofsolvents. The other electroactive material may be selected from anemissive material or a charge transport material, for example. Byappropriate selection of the other electroactive material, it has beenfound that after deposition, the hole transport material and the otherelectroactive material may phase separate to form two layers of thedevice; the hole transport material phase separating to form the holetransport layer on the conducting layer and the at least one otherelectroactive material forming a further electroactive layer on the holetransport layer.

EXAMPLE 1

A monomer for preparing a polymer soluble in a polar solvent may beprepared according to the following scheme.

The bromine substituents may be replaced with boronic acid or estergroups, to form Monomer 1 shown below, and polymerised with dibromo-TFBto form Polymer 1 in accordance with the method disclosed in WO00/53656:

A layer of PEDT/PSS, available from H C Starck as Baytron P® wasdeposited by spin coating onto an indium tin oxide anode supported on aglass substrate (available from Applied Films, Colorado, USA) Polymer 1was deposited onto the PEDT/PSS layer by spin coating from methanolsolution, followed by deposition of an electroluminescent layer ofpoly-9,9-di(n-octyl)fluorene from xylene solution. A cathode was formedby evaporating onto the electroluminescent layer a first layer of bariummetal and a capping layer of aluminium. The device was sealed using anairtight metal container available from Saes Getters SpA.

EXAMPLE 2

A monomer for preparing a polymer soluble in a polar solvent may beprepared according to the following scheme.

The bromine substituents may be replaced with boronic acid or estergroups, to form Monomer 3 shown below, and polymerised with dibromo-TFBto form Polymer 2 in accordance with the method disclosed in WO00/53656:

A layer of PEDT/PSS, available from H C Starck as Baytron P® wasdeposited by spin coating onto an indium tin oxide anode supported on aglass substrate (available from Applied Films, Colorado, USA) Polymer 2was deposited onto the PEDT/PSS layer by spin coating from methanolsolution, followed by deposition of an electroluminescent layer ofpoly-9,9-di(n-octyl)fluorene from xylene solution. A cathode was formedby evaporating onto the electroluminescent layer a first layer of bariummetal and a capping layer of aluminium. The device was sealed using anairtight metal container available from Saes Getters SpA.

EXAMPLE 3

A monomer for preparing a polymer soluble in a polar solvent may beprepared according to the following scheme.

The bromine substituents may be replaced with boronic acid or estergroups, to form Monomer 5 shown below, and polymerised with dibromo-TFBto form Polymer 3 in accordance with the method disclosed in WO00/53656:

A layer of PEDT/PSS, available from H C Starck as Baytron P® wasdeposited by spin coating onto an indium tin oxide anode supported on aglass substrate (available from Applied Films, Colorado, USA) Polymer 3was deposited onto the PEDT/PSS layer by spin coating from methanolsolution, followed by deposition of an electroluminescent layer ofpoly-9,9-di(n-octyl)fluorene from xylene solution. A cathode was formedby evaporating onto the electroluminescent layer a first layer of bariummetal and a capping layer of aluminium. The device was sealed using anairtight metal container available from Saes Getters SpA.

EXAMPLE 4 2-Step Synthesis of A9 Dibromide Shown in the Reaction SchemeBelow

4.1 N-(6-bromohexyl)morpholine

Under nitrogen 250 ml anhydrous THF were added to 37 g (1.1 eq, 385mmol) sodium tert-butoxide. Then 30.45 g (1 eq, 350 mmol) morpholinewere added neat. The suspension was heated to 50° C. for 1 h. Aftercooling to RT, 1.2 l anhydrous THF and 85.29 g (1 eq, 350 mmol)dibromohexane in ˜150 ml anhydrous THF were added. After 1 h at RT themixture was heated to 85° C. over night. The overstanding solution wasdecanted and all volatiles removed in vacuo. The residue was dissolvedin ether and water and the organic layer extracted with 2M hydrochloricacid. After dilution with water and ether, KOH flakes were added undervigorous stirring and cooling until pH=10. After phase separation, theaqueous layer was extracted with ether. The combined organic layers weredried over brine and MgSO4 and all volatiles removed to yield 40 g.Further purification by column chromatography (70% hexane, 30% ethylacetate, 5% triethylamine) yielded 14.56 g, 99% by GCMS. 1H-NMR (400MHz, CDCl3): □ [ppm]=3.71 (t, J=4 Hz, 4H), 3.41 (t, J=6.8 Hz, 2H), 2.42(t, J=4 Hz, 4H), 2.32 (t, J=7.6 Hz, 2H), 1.48 (m, 4H), 1.34 (m, 2H).

4.2 2,7-Dibromo-9,9′-bis-(6-(N-morpholinyl)hexyl)fluorene

A mixture of 24.5 g (2.5 eq, 98 mmol) N-(6-bromohexyl)morpholine, 12.7 g(1 eq, 39 mmol) 2,9-dibromofluorene, and 170 mg (0.01 eq, 0.4 mmol)Aliquat 336 was heated to 80° C. 11 g (5 eq, 196 mmol) KOH in 25 mlwater were added. After 18 h the crude reaction mixture was diluted withdichloromethane and water. After phase separation the organic layer waswashed with water, dried over brine and MgSO4 and all volatiles removedin vacuo. Further purification by column chromatography (70% hexane, 30%ethyl acetate, 5% triethylamine) and recrystallisation from methanolyielded 8 g (31% yield) pale yellow crystals (plates), 100% pure byhigh-sensitivity GCMS. ¹H-NMR (400 MHz, CDCl3): □ [ppm]=7.48 (m, 4H),7.43 (s, 2H), 3.68 (t, J=4.8 Hz, 8H), 2.35 (t, J=4 Hz, 8H), 2.19 (t, J=8Hz, 4H), 1.91 (m, 4H), 1.29 (m, 4H), 1.08 (m, 8H), 0.59 (m, 4H).

4.3

The A9 dibromide monomer may be used in a Suzuki polymerisation reactionto form an electroactive polymer. The polymer containing the repeatunit:

is capable of being protonated by a conducting material, such as PEDTdoped with a charge balancing dopant. The charge balancing dopant may beacidic. The charge balancing dopant may be a polyanion. Preferably thecharge balancing dopant comprises a sulfonate, such as poly(styrenesulfonate) (PSS) where the PEDT conducting polymer is blended withacidic polar PSS groups.

Thus, when the polymer is deposited onto a layer of PEDT/PSS, theprotonation interaction results in a stable A9 polymer layer on whichfurther layers may be deposited.

EXAMPLE 5

An AB copolymer comprising 50% of the A9 repeat unit of Example 4 and50% of the TFB repeat unit was prepared by Suzuki polymerisationaccording to the method described in WO 00/53656.

EXAMPLE 6

A layer of PEDT/PSS, available from H C Starck as Baytron P® wasdeposited by spin coating onto an indium tin oxide anode supported on aglass substrate (available from Applied Films, Colorado, USA). TheA9-TFB polymer of example 5 was deposited over the PEDT/PSS layer byspin-coating from xylene solution and the solvent was evaporated to forma 170 nm thick layer of A9-TFB polymer.

This layer of was subjected to continuous spin-rinsing with xylene untilthe thickness of the layer remained constant even with further rinsing,after which a 77 nm thick film of A9-TFB remained.

For the purpose of comparison, a 1:1 copolymer of 9,9-dioctylfluoreneand TFB was deposited on a PEDT/PSS film and spin rinsed in the sameway, after which none of the comparative copolymer layer remained, thusdemonstrating the insolubilising effect of the polar substituent groupof the A9-TFB copolymer.

EXAMPLE 7

A layer of PEDT/PSS, available from H C Starck as Baytron P® wasdeposited by spin coating onto an indium tin oxide anode supported on aglass substrate (available from Applied Films, Colorado, USA). A blendof the A9-TFB polymer of example 5 and poly(9,9-dioctylfluorene) wasdeposited over the PEDT/PSS layer by spin-coating from xylene solution.The blend underwent vertical phase separation to form a bilayer of anA9-TFB hole transporting layer and an emissive layer ofpoly(9,9-dioctylfluorene). A cathode was deposited over the emissivelayer and the device was sealed in accordance with the method of Example3.

1. A semiconductive hole transport material containing polar substituentgroups, the polar substituent groups substantially not affecting theelectronic properties of the hole transport material and the holetransport material being soluble in a polar solvent.
 2. A materialaccording to claim 1, wherein the nature and number of polar substituentgroups are selected such that the hole transport material is soluble ina polar solvent having a dielectric constant at 20° C. of greater than15.
 3. A material according to claim 1, wherein the polar substituentgroups independently are selected from aliphatic or alicyclic oxygen-,nitrogen-, sulphur- and phosphorous-containing groups.
 4. A materialaccording to claim 1 wherein the polar substituent groups comprise aplurality of groups XY, where XY represents a group with a highdissociation constant such that it is ionized completely.
 5. A materialaccording to claim 1 wherein the hole transport material comprises ahole transport polymer.
 6. A material according to claim 5, wherein thehole transport polymer comprises an aryl or heteroaryl repeat group Ar.7. A material according to claim 6, wherein Ar represents fluorene,spirofluorene, indenofluorene, phenylene, phenylenevinylene, thiophene,benzothiadiazole or triarylamine.
 8. A material according to claim 6,wherein Ar is present in a side group that is pendant from the polymerbackbone.
 9. A material according to claim 8, wherein the hole transportpolymer contains a repeat side group comprising formula 13:

where Ar represents an aryl or heteroaryl group and R represents a polarsubstituent group.
 10. A material according to claim 8, wherein therepeat side group is attached to a non-conjugated region in the polymerbackbone.
 11. A material according to claim 10, wherein the holetransport polymer comprises a repeat unit of formula 20:

where Ar and R are as defined in claim
 9. 12. A material according toclaim 6, wherein Ar is present in the polymer backbone.
 13. A materialaccording to claim 12, wherein the hole transport polymer comprises arepeat unit comprising general formula 25:

where Ar represents an aryl or heteroaryl group; x represents anoptional organic spacer group; and R represents a polar substituentgroup.
 14. A material according to claim 13, wherein x comprises a groupwhich breaks any conjugation between R and Ar.
 15. A material accordingto claim 13, wherein x is selected from aryl; heteroaryl; alkyl; alkoxy;and perfluoroalkyl.
 16. A material according to claim 13, wherein Arrepresents fluorene.
 17. A material according to claim 16, wherein thehole transport polymer comprises a repeat unit general formula 1:

where x and x′ are optional organic spacer groups; R and R′ are polarsubstituent groups; and n4 and n5 each independently is in the range offrom 0 to
 5. 18. A material according to claim 13, wherein the polymercontains a further aryl or heteroaryl repeat unit.
 19. A materialaccording to claim 18, wherein the further repeat unit is a triarylaminerepeat unit or a fluorene repeat unit.
 20. A method for forming anorganic electronic device, including the steps of: depositing asemiconductive hole transport material from solution in a polar solventto form a hole transport layer; and subsequently forming a second layerby depositing on the hole transport layer a second material fromsolution in a non-polar solvent in which the hole transport layer issubstantially insoluble; and characterised in that the hole transportmaterial contains polar substituent groups selected so that the holetransport material is soluble in the polar solvent, the second materialbeing substantially insoluble in the polar solvent.
 21. (canceled)
 22. Amethod according to claim 20, wherein the organic electronic devicecomprises a light-emitting device (LED).
 23. A method according to claim20, wherein the second material is a polymer.
 24. A method according toclaim 20, wherein the second material is a light emissive material. 25.An organic electronic device obtained by the method defined in claim 20.26. An organic electronic device containing a hole transport layercomprising a semiconductive hole transport material as defined inclaim
 1. 27. (canceled)
 28. A method for forming an organic electronicdevice, including the steps of: depositing a first polymer from solutionin a first solvent to form a first layer of the device; and subsequentlyforming a second layer of the device by depositing a second polymer fromsolution in a second solvent in which the first layer is substantiallyinsoluble; where either the first solvent or the second solvent is apolar solvent; and where the first polymer or the second polymercontains polar substituent groups selected so that the first polymer orthe second polymer is soluble in the polar solvent, the other of thefirst polymer and the second polymer being substantially insoluble inthe polar solvent; and characterised in that the first polymer comprisesa repeat unit Ar1 and the second polymer comprises a repeat unit Ar2,where Ar1 and Ar2 comprise the same aryl or heteroaryl group.
 29. Amethod according to claim 28, wherein the aryl and heteroaryl groupcomprised in Ar1 and Ar2 is selected from fluorene, phenylene,phenylenevinylene, benzothiadiazole, thiophene, triarylamine,indenofluorene, and spirofluorene.
 30. A method according to claim 28,wherein whichever of the first polymer and the second polymer issubstantially insoluble in the polar solvent, is deposited from solutionin a non-polar solvent.
 31. A method according to claim 28, wherein thefirst polymer and the second polymer are conjugated.
 32. A methodaccording to claim 31, wherein there is a break in the conjugationbetween each polar substituent group and the conjugated segment orsegments in whichever of the first polymer and the second polymer issoluble in the polar solvent.
 33. A method according to claim 31,wherein a spacer group is present between a polar substituent group andthe conjugated segment or segments in whichever of the first polymer andthe second polymer is soluble in the polar solvent.
 34. A methodaccording to claim 28, wherein whichever of the first polymer and thesecond polymer is soluble in the polar solvent, comprises a fluorenerepeat unit having at least one polar substituent group.
 35. An organicelectronic device obtained by the method as defined in claim
 28. 36. Amethod for forming an organic electronic device, including the steps of:forming a conducting layer comprising a conducting material, saidconducting material containing polar groups; and forming a holetransport layer comprising a semiconductive hole transport material onthe conducting layer, said hole transport material containing polarsubstituent groups.
 37. A method according to claim 36, wherein theconducting material comprises a conducting polymer.
 38. A methodaccording to claim 37, wherein the conducting material comprisespoly(ethylene dioxythiophene)/poly-(styrene sulfonate) (PEDT/PSS).
 39. Amethod according to claim 36, wherein the method further includes thestep of depositing a third layer comprising a third material on the holetransport layer by processing from solution in a solvent in which thehole transport layer is soluble in the absence of the conducting layer.40. An organic electronic device obtained by the method as defined inclaim
 36. 41. A method according to claim 3, wherein the solarsubstitutent groups, independently are selected for the groupsconsisting of polyether, hydroxyl, ester, acid, amine, cyano, amide,imine, sulfonate, and sulfate groups.